FIG. 1 schematically shows a conventional structure of a detector sensitive to ionizing radiation. Such a detector comprises a conductive tube 1 filled with a gas mixture, sealed at its ends by isolating plugs 3. A conductive wire 5 having its ends crossing plugs 3 in an air-tight fashion, is pulled tight at the center of tube 1 by a spring 7 located within the tube. A positive electric voltage applied to wire 5 by a measurement circuit 9 enables an electric field to be defined within the tube, which encourages the drift and amplification of electrons generated by the passing of the ionizing radiation.
The gas mixture contained in the tube is chosen such that it is ionized by the particles to be detected, either directly, or after conversion into ionizing particles. For example, for neutron detection, a mixture of CF4 and of 3He (helium-3) in which 3He behaves as a converter and CF4 as a gas for stopping the two ionizing particles (proton and triton) emitted after the capture of a neutron by a 3He atom may be used.
A so-called charge division process is currently used to measure the position of the impact along the tube. The wire is then resistive. The measurement circuit comprises read electronics enabling to measure the charge signal amplitude at each end of the wire. This detection method is always complex. Another so-called “counting” operating mode uses electronics based on the comparison of the signal measured at a single end of the wire with a reference voltage. This detection mode is generally inaccurate in its current implementations.
The uniformity of the detector response is affected by the inaccuracy of the wire centering inside of the tube, and such a centering is difficult to achieve. The difficulty of centering wire 5 limits the maximum amplification gain with which the detector can operate, which has direct consequences upon the detector performance (energy and position resolution).
An ionizing radiation detector is conventionally formed of several elementary detectors having juxtaposed tubes. The operation of a detector depends on the quality and on the pressure of the gas mixture that it contains. Furthermore, when several detectors must be used together with a certain minimum space between tubes, which is typically 10 millimeters (mm), it is difficult to ensure the continuity of the electromagnetic field shielding between the tube sheet and measurement circuit 9 without exceeding the external diameter of the tube, which results in creating dead spaces between detectors, thus resulting in a loss of sensitivity of the assembly.